Many brokerage firms, such as E-Trade, Fidelity, Schwab and Vanguard, cover 100% of any losses in your accounts due to unauthorized activity. Ask your broker about its security measures and guarantee, and take the steps it recommends to protect your account, such as using strong passwords and a unique user name, as well as installing up-to-date antivirus software on your computer. If you notice suspicious activity in your account, contact the firm immediately. In submitting a claim, you may need to complete a notarized affidavit explaining the unauthorized activity or provide a copy of a police report.

If you share your user name, password or answers to security questions with a person or service—say, a financial adviser or an aggregator site, such as Mint—you may have a tougher time getting the brokerage to pay a claim if money is stolen through a data breach at the third party.